AP Psychology – Nervous System (CNS, PNS, Sympathetic/Parasympathetic)

AP Psychology – Nervous System (CNS, PNS, Sympathetic/Parasympathetic)

AP Psychology Study Guide: The Nervous System (CNS, PNS, Sympathetic/Parasympathetic)

What This Is

The nervous system is your body’s electrochemical communication network, controlling everything from reflexes to emotions. It’s divided into the central nervous system (CNS—brain and spinal cord) and the peripheral nervous system (PNS—nerves outside the CNS). The PNS further splits into the somatic (voluntary movements) and autonomic (involuntary functions) systems, with the autonomic system having two key branches: sympathetic (fight-or-flight) and parasympathetic (rest-and-digest). This topic is high-yield on the AP exam—expect multiple-choice questions and FRQs on how these systems interact (e.g., "Explain how the sympathetic nervous system prepares the body for stress").

Real-world example: Imagine you’re about to give a speech. Your sympathetic nervous system kicks in—your heart races, pupils dilate, and digestion slows. Afterward, your parasympathetic nervous system calms you down, lowering your heart rate and resuming digestion. This back-and-forth is how your body maintains homeostasis (balance).

Key Terms & Concepts

• Nervous System: The body’s speedy, electrochemical communication network, consisting of all nerve cells.
• Central Nervous System (CNS): The brain and spinal cord; the body’s decision-maker.
• Peripheral Nervous System (PNS): Nerves outside the CNS that connect it to the rest of the body. Divided into somatic and autonomic systems.
• Somatic Nervous System: Controls voluntary movements (e.g., raising your hand) by sending messages to skeletal muscles.
• Autonomic Nervous System (ANS): Controls involuntary functions (e.g., heartbeat, digestion). Split into sympathetic and parasympathetic divisions.
• Sympathetic Nervous System: The "fight-or-flight" system; arouses the body in stressful situations (e.g., increases heart rate, dilates pupils, slows digestion).
• Parasympathetic Nervous System: The "rest-and-digest" system; calms the body after stress (e.g., lowers heart rate, stimulates digestion).
• Reflex: A simple, automatic response to a stimulus (e.g., pulling your hand away from a hot stove). Controlled by the spinal cord (not the brain).
• Neuron: A nerve cell; the basic building block of the nervous system. Transmits signals via action potentials (electrical impulses).
• Neurotransmitters: Chemical messengers that cross the synapse (gap between neurons) to transmit signals. Examples:
• Acetylcholine (ACh): Enables muscle action, learning, and memory (low ACh-Alzheimer’s).
• Norepinephrine: Helps control alertness and arousal (linked to the sympathetic nervous system).
• Homeostasis: The body’s tendency to maintain a balanced internal state (e.g., temperature, blood sugar). The ANS helps regulate this.
• Endocrine System: The body’s slow chemical communication system (hormones in the bloodstream). Works with the nervous system (e.g., adrenaline from the adrenal glands during fight-or-flight).

Step-by-Step: How the Nervous System Works in a Stressful Situation

Use this process to analyze a scenario (e.g., FRQ: "Explain how the nervous system responds when someone sees a snake").

1. Stimulus Detection: Sensory neurons (PNS) detect the threat (e.g., seeing a snake).
2. Signal Transmission to CNS: The sensory neurons send the signal to the spinal cord (for reflexes) or brain (for conscious processing).
3. Brain Processing: The thalamus relays the signal to the amygdala (fear center) and hypothalamus (activates the ANS).
4. Sympathetic Activation: The hypothalamus triggers the sympathetic nervous system, releasing norepinephrine and adrenaline (from the adrenal glands).
5. Physiological Response: Heart rate increases, pupils dilate, digestion slows, and blood sugar rises (preparing for action).
6. Parasympathetic Recovery: After the threat passes, the parasympathetic nervous system takes over to calm the body (e.g., heart rate slows, digestion resumes).

Common Mistakes

• Mistake: Confusing the somatic and autonomic nervous systems.

• Correction: The somatic system controls voluntary movements (e.g., walking), while the autonomic system controls involuntary functions (e.g., heartbeat). Why? The somatic system connects to skeletal muscles; the autonomic system connects to organs/glands.

• Mistake: Thinking the sympathetic system is always "bad" and the parasympathetic is always "good."

• Correction: Both systems are essential for survival. The sympathetic system prepares you for action (e.g., running from danger), while the parasympathetic system conserves energy (e.g., sleeping). Why? They work together to maintain homeostasis.

• Mistake: Forgetting that reflexes are controlled by the spinal cord, not the brain.

• Correction: Reflexes (e.g., knee-jerk, pulling hand from heat) are automatic and bypass the brain for speed. Why? The spinal cord acts as a shortcut to prevent injury.

• Mistake: Mixing up neurotransmitters and hormones.

• Correction: Neurotransmitters (e.g., dopamine) are fast-acting and work in the nervous system, while hormones (e.g., adrenaline) are slower and travel through the bloodstream (endocrine system). Why? They have different pathways and speeds.

• Mistake: Assuming the endocrine system is part of the nervous system.

• Correction: The endocrine system is a separate (but interconnected) system that uses hormones instead of electrical signals. Why? The hypothalamus (brain) links the two systems.

AP Exam Insights

• Tricky Distinction: Sympathetic vs. Parasympathetic

• The AP exam loves asking about these two systems. Remember:

  • Sympathetic = "Stress" (e.g., "What happens to digestion during a scary movie?"-slows down).
  • Parasympathetic = "Peace" (e.g., "What happens to heart rate after a meal?"-slows down).

• FRQ Hot Topic: Expect a scenario-based FRQ where you must:

• Identify which nervous system is active (e.g., "Explain how the sympathetic nervous system prepares the body for a job interview").
• Describe specific physiological responses (e.g., increased heart rate, pupil dilation).

• Compare it to the parasympathetic response afterward.

• Multiple-Choice Trap: Questions may ask about neurotransmitters in the context of the nervous system. For example:

• "Which neurotransmitter is most associated with the sympathetic nervous system?"-Norepinephrine (not dopamine or serotonin).

• Real-World Application: The exam may link this to stress, emotions, or disorders (e.g., "How might an overactive sympathetic nervous system contribute to anxiety?").

Quick Check Questions

1. Multiple Choice: Which division of the autonomic nervous system is responsible for slowing heart rate and stimulating digestion?
2. A) Sympathetic
3. B) Parasympathetic
4. C) Somatic
5. D) Central

6. Answer: B) Parasympathetic. Explanation: The parasympathetic system calms the body after stress ("rest-and-digest").

7. Short FRQ: A student is about to take a final exam. Describe two physiological responses caused by the sympathetic nervous system and one caused by the parasympathetic nervous system after the exam.

8. Sample Answer:

   • Sympathetic: Increased heart rate (to pump blood faster) and dilated pupils (to improve vision).
   • Parasympathetic: Slowed heart rate (to return to baseline).

9. Multiple Choice: Which of the following is controlled by the somatic nervous system?

10. A) Heartbeat
11. B) Digestion
12. C) Raising your hand
13. D) Pupil dilation
14. Answer: C) Raising your hand. Explanation: The somatic system controls voluntary movements of skeletal muscles.

Last-Minute Cram Sheet

1. CNS = Brain + Spinal Cord (decision-maker).
2. PNS = Everything else (nerves outside CNS).
3. Somatic = Voluntary (e.g., walking, talking).
4. Autonomic = Involuntary (e.g., heartbeat, digestion).
5. Sympathetic = "Fight-or-flight" (? heart rate,-digestion).
6. Parasympathetic = "Rest-and-digest" (? heart rate,-digestion).
7. Reflexes = Spinal cord (not brain!).
8. Neurotransmitters = Fast (e.g., ACh, norepinephrine); Hormones = Slow (e.g., adrenaline).
9. Homeostasis = Balance (ANS maintains it).
10. Don’t mix up sympathetic/parasympathetic! (Sympathetic = Stress, Parasympathetic = Peace).